There is an ever increasing need for data storage devices having greater storage capacity with smaller form factors for multimedia systems utilizing text, video, and audio information. Further, there is a large demand for highly portable, rugged, and robust systems for use as multimedia entertainment, storage systems for PDAs, cell phones, electronic books, and other systems. One of the more promising technologies for rugged, removable, and portable data storage is WORM (write once read many) optical disk drives.
One of the important factors affecting design of an optical system (such as that utilized in a WORM drive) is the optical components utilized in the system and the control of actuators utilized to control the optical system on the disk. The optical system typically includes a laser or other optical source, focusing lenses, reflectors, optical detectors, and other components. Although a wide variety of systems have been used or proposed, typical previous systems have used optical components that were sufficiently large and/or massive that functions such as focus and/or tracking were performed by moving components of the optical system.
Many early optical disks and other optical storage systems provided relatively large format read/write devices including, for example, devices for use in connection with 12 inch (or larger) diameter disks. As optical storage technologies have developed, however, there has been increasing attention toward providing feasible and practical systems which are relatively smaller in size. Generally, a practical read/write device must accommodate numerous items within its form factor, including the media, media cartridge (if any), media spin motor, power supply and/or conditioning, signal processing, focus, tracking or other servo electronics, and components associated or affecting the laser or light beam optics. Accordingly, in order to facilitate a relatively small form-factor, an optical head occupying small volume is desirable. In particular, it is desirable for a small optical head in the direction perpendicular to the surface of the spinning media.
Additionally, a smaller, more compact, optical head provides numerous specific problems for electronics designed to control the position and focus of the optical head including: the need for extensive drive calibration and periodic drive recalibration, time critical servo state machines to compensate for the flexible focus and tracking actuators, nonlinear and cross-coupled tracking and focus position sensors, dynamic cross-coupling between the multiple servo loops, need for low power consumption to conserve battery life, removable and interchangeable media, robust handling of media defects, presence of both pre-mastered and user writeable areas on the same disk, need to operate in wide range of conditions including various physical orientations, wide range of ambient temperatures and humidity levels, and the presence of shock and vibration.
Therefore, there is a need for an optical head with a small form factor and, in addition, a servo system for controlling the head so that data can be reliably read from and written to the optical media.